RIVER GAUGE · MAINSTREAM DEEP TUNNEL
Mainstream Deep Tunnel at McCook Reservoir
Cook County, Illinois
Water level-221.00 ft
Flow—
Last readingSep 16, 2026, 12:00 PM UTC (last recorded)
Action-100 ft
Minor flood-30 ft
The past week
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What floods at each level
- -22 ft
Lowest rim of McCook Reservoir.
- -40 ft
McCook Reservoir reaches 100 percent of full storage. Combined sewer overflow event likely in central Cook County. Water remains contained within the reservoir.
- -95 ft
McCook Reservoir reaches 75 percent of full storage. Combined sewer overflow event possible in central Cook County.
- -155 ft
McCook Reservoir reaches 50 percent of full storage.
- -215 ft
McCook Reservoir reaches 25 percent of full storage.
- -280 ft
McCook Reservoir is empty, 0 percent of full storage.
Highest crests on record
| Date | Level | Flow |
|---|---|---|
| Apr 15, 2026 | -33.7 ft | — |
| Jul 5, 2026 | -34.5 ft | — |
| Apr 4, 2026 | -35 ft | — |
More on Mainstream Deep Tunnel
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